1. Field of the Invention
The present invention relates to a method of and an apparatus for focusing an image in a television camera for video telephone, and more particularly to a method of and an apparatus for focusing an image, to be transmitted, in a television camera for video telephone through a simple process.
2. Description of the Prior Art
The recent development of the ISDN (integrated services digital network) allows information to be transmitted over a wide range of frequencies and also makes video telephone practically feasible. The video telephone system includes television cameras at terminals for imaging speakers and any documents or materials at hand so that the other parties can visually perceive them on CRT (cathode-ray tube) displays.
To image a document, for example, at hand, the user of the CRT display switches from a reception mode to a transmission mode, directs the television camera, detached from the video telephone set, to image the document that may be placed on a desk or the like, and focuses the displayed image by turning the lens barrel of the television camera white viewing the image on the CRT display.
It is cumbersome to turn the lens barrel with one hand in focusing the displayed image, and it is also difficult to tell exactly when the displayed image is sharply focused based on the visual check of the image on the CRT display.
To solve the above problems, it has been proposed to combine an automatic focusing mechanism with the television camera for automatically focusing the image. However, the added automatic focusing mechanism makes the entire television camera system quite complex. The television camera system with the automatic focusing mechanism is made up of a large number of parts, highly costly, and large in size. Some automatic focusing mechanisms require more time in getting images focused than manual focusing mechanisms.